Winter is a fine time to dream about summer.
I dream of spending a week or so, someday, bicycling in northern Idaho. There are some fabulous opportunities that aren't very well publicized. If you love mingling with big crowds, look elsewhere. (Except Coeur d'Alene... sadly, it has evolved into a Strip-mall Suburbia.)
Take, for example, the 72-mile-long paved rail-to-trail called the Trail of the Coeur d'Alenes. To find it, find Interstate 90 in north Idaho. The Trail runs roughly parallel, a few miles to the south, from Plummer near the Washington border to Mullan near the Montana border.
My dream is to start at the Plummer end (at the bottom of the hill!) and ride eastward, taking maybe 3 days to explore the attractions along the route... then returning the entire 72 miles in one day. Maybe alternate between camping and motels, like I do on motorcycle adventures.
Attractions along the way include Heyburn State Park, a bridge-crossing at the south end of Lake Coeur d'Alene, miles and miles of lakefront and river-side riding, and numerous historic sites along the way (Cataldo Mission, mining-town Wallace, etc.). I'd suggest getting off at Wallace, and taking a ride up the (dirt) Burke Road, to see the remnants of little mining towns like Frisco and Black Bear.
Much more information can be found here, including "Google Earth flyover" views, that should convince you this is a GOOD idea.
When you get done with the Coeur d'Alene trail, try the Route of the Hiawatha. It, too, is built on an abandoned railway. But it's not paved, but rather well-packed dirt. (At least, the one time I rode it.) And, it goes through awesome tunnels and over even-more-awesome trestles. (If you're afraid of the dark, or suffer from "high anxiety," this one may not be for you... although there is essentially no real danger unless you're just being stupid.)
My family tried it 8 or so years ago, and it was a fantastic day ride! I dropped them off at the top, then drove to the bottom and parked the shuttle craft. Then I rode my bicycle furiously up the (car) road... then we all road down the trail together.
Since we rode it, they've completed work on the Taft Tunnel, and have opened it for bicycle use. The tunnel is approximately 1.5 miles - when you enter, you're in Idaho; when you emerge, you're in Montana! (Headlights and helmets are required... believe me about the headlights... or at least a good flashlight.)
It costs a few bucks to ride - $9 for a day pass as of 2007 - but it's a small price to pay, and they use the money to keep the trail well-maintained. If you're in any kind of bike-riding shape, I'd suggest you consider riding UP the trail in the morning, eating a packed-along lunch at the top, then riding back down in the afternoon.
More info can be found here.
We've talked very casually about going back as a family and spending several days bicycling. But I'm afraid they're somewhat deterred by the notion of going places by self-power. At least for day after day. I'm pretty confident even casual cyclists could do these rides - since trains used to run along the same paths, they're never steep inclines. So it's just a matter of setting the proper pace.
There is much more to see and do in northern Idaho... it's a whole different world from southern Idaho up there.
If you need to ride something besides a bicycle for a day, check out the Silverwood Theme Park, kind of a poor man's Knott's Berry Farm, with a sweet wooden roller coaster and other exciting rides. It's a few miles north of Coeur d'Alene.
[NOTES: Just in case you're concerned about the "Bike Nazi" promoting an area that was, unfortunately, synonymous with the Nazi/Skinhead movement a few years back... I am NOT associated with those people in any way. And besides, most of 'em got run out of town a few years back. I found the "Hiawatha" photo at the TourVelo website.]